Such a fastening device, in which a penetrating die is driven by means of a chop hammer by a fitter, is known. Such manual insertion of fastening staples is often inadequate due to the hammering force being irregular. If the hammering force is excessive, there is a risk that the fastening staples are inserted too deeply into the belt ends, damaging the fastening clips and/or their legs or even fracturing them. Another problem can be seen in the fact that the pressure head could pop up under excessive hammering of the penetrating dies due to bouncing back, leading to projection of the fastening staples from the belt ends, being neither hammered nor penetrating the belt ends to a sufficient depth and not accurately enough. Moreover, even damage of the pressure head cannot be excluded as the hammer will not always be driven exactly vertically unto the penetrating die but may hit it obliquely, with the hammer hitting the pressure head at the same time. Finally, difficulties could also occur when the fastening staples are to penetrate very thick belt ends.